Axle driving unit for a lawn tractor

ABSTRACT

An axle driving unit having a housing ( 21, 22 ) for supporting a first axle ( 17 ) for mounting thereon a first driving wheel ( 3 L), and a longer second axle ( 18 ) for mounting thereon a second driving wheel ( 3 R). The axle driving unit is eccentrically mounted on a body frame ( 1 ) in proximity to the first driving wheel ( 3 L). A speed change transmission (T) is disposed in an enlarged region of the housing that extends substantially perpendicularly with respect to the axles ( 17, 18 ). The axle driving unit can thus be easily disposed to the side of a chute ( 6 ) of a rear-discharge type lawn tractor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an axle driving unit suitablefor use with a rear-discharge lawn tractor having a mower locatedbeneath the body of the tractor between the front and rear wheels.

[0003] 2. Related Art

[0004] U.S. Pat. No. 3,969,876 discloses a conventional lawn tractorhaving a rear discharge system, which has a mower driven by a primemover mounted on it, and a leaf blower loaded on the rear portion of thetractor. The rear discharge system disposes a chute, for discharginglawn grass cut by the mower, longitudinally between the left and rightrear wheels. The rear discharge system has no projection to the outsideof the body of the tractor. The cut lawn grass is discharged directlyrearwardly of the tractor. This has the advantage of eliminatingequipment, such as an auxiliary suction fan.

[0005] However, because the space between the left and right rear wheelsis very narrow, it is very difficult to laterally juxtapose therebetweenthe cut grass chute and an axle driving apparatus. As disclosed in U.S.Pat. No. 3,969,876, a hydraulic stepless speed change transmission and adifferential gear constituting the axle driving unit are separated andare housed in separate housings. The differential gear is disposed inthe narrow space between the wheels, and the transmission is disposed atanother position on the body of the tractor. The output shaft of thehydraulic stepless speed change transmission and differential gear areconnected by a chain belt mechanism. Accordingly, the axle driving unithas the disadvantages of a high manufacturing cost and a long assemblytime. Also, since one axle, through which the cut grass chute passes, ismuch longer than the other axle, this design has the furtherdisadvantage that the one longer axle is easy to deflect. Accordingly,the life span of a bearing for the one longer axle provided at thedifferential gear is reduced.

[0006] An axle driving unit which houses in a common housing a hydraulicstepless speed change transmission and a differential gear fordifferentially connecting a pair of axles and integrates them iswell-known, as disclosed in, for example, U.S. Pat. No. 4,914,907 andU.S. Pat. No. 4,932,209. In these patents, the transmission comprises acombination of a variable displacement type hydraulic pump and a fixeddisplacement hydraulic motor. The hydraulic pump and motor are mountedside by side and longitudinally of the axle with respect to anL-like-shaped center section, whereby the entire axle driving unit islarger in width longitudinally of the axle. Hence, the axle driving unitof this design interferes with the chute of a lawn tractor which has arear discharge system. As a result, the chute cannot be disposed betweenthe left and right rear wheels.

SUMMARY OF THE INVENTION

[0007] The axle driving unit of the present invention is constructed sothat a first shorter axle that mounts a first driving wheel, and asecond longer axle that mounts a second driving wheel are supported by ahousing provided on a body frame. The housing is attached to the tractorbody frame so that it is eccentric or offset to be in proximity to thefirst driving wheel. The housing is provided with an enlarged regionextending forward at approximately a right angle with respect to theaxles. A hydraulic stepless speed change transmission is provided in theenlarged region. As a result, the axle driving unit of the presentinvention can be easily disposed laterally of (or to the side of) thechute of a lawn tractor of the rear discharge type.

[0008] In order to improve the operating efficiency of the hydraulicstepless speed change transmission, it is desirable to construct thetransmission so that it is a hydraulic stepless system fluidlyconnecting the hydraulic pump and hydraulic motor to each other. In thiscase, the hydraulic pump can be disposed in the enlarged region, smallerin width and spaced apart from the axle, and the hydraulic motor can bedisposed in proximity to the axle.

[0009] In the enlarged region are provided a pump mounting surface and amotor mounting surface disposed substantially perpendicular orrectangular with respect to each other for mounting the hydraulic pumpand hydraulic motor. It is preferable that the hydraulic pump is mountedonto the pump mounting surface so that an input shaft connected to thehydraulic pump is oriented approximately vertically with respect to theaxles, and the hydraulic motor is mounted onto the motor mountingsurface so that an output shaft connected to the hydraulic motor isoriented approximately horizontally with respect to the axles. In a lawntractor that includes a prime mover having a vertical crankshaft, theinput shaft of the transmission can be connected therewith by use of asimple belt transmitting mechanism. The output shaft of the transmissioncan be connected with the axle by use of an inexpensive spur gear havinga low manufacturing cost.

[0010] Bearing means are provided in the housing for supporting thefirst and second axles. A pair of bearing holding portions forsupporting distal portions of the first and second axles define thewidth of the housing to be smaller than the length of the housingincluding the enlarged region. As a result, the enlarged region iselongated so that the chute can have as large a cross-sectional area aspossible.

[0011] It is desirable that the second longer axle be supported at anintermediate portion thereof by a bearing device provided on the tractorbody frame. As a result, the second longer axle is stably supported. Itis also desirable that the second axle be composed of at least two axleparts separably connected with each other through a coupling. Hence, theaxle driving unit becomes superior in assembly efficiency andtransformation efficiency. The axle to which the other (first) drivingwheel is mounted is stably supported by a bearing device provided on thetractor body frame.

[0012] The above and further objects and novel features of the inventionwill more fully appear from the following detailed description when thesame is read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 a side view of a lawn tractor of the present invention,

[0014]FIG. 2 is a cross sectional view of the lawn tractor of FIG. 1taken along line 2-2,

[0015]FIG. 3 is a cross sectional view taken along line 3-3 in FIG. 2,

[0016]FIG. 4 is a cross sectional view taken along line 4-4 in FIG. 3showing a first embodiment of the axle driving unit, from which an upperhalf housing is removed,

[0017]FIG. 5 is a sectional view taken on the line 5-5 in FIG. 4,

[0018]FIG. 6 is a sectional view taken on the line 6-6 in FIG. 4,

[0019]FIG. 7 is a sectional view taken on the line 7-7 in FIG. 4,

[0020]FIG. 8 is a sectional view taken on the line 8-8 in FIG. 4,

[0021]FIG. 9 is a sectional view taken on the line 9-9 in FIG. 8,

[0022]FIG. 10 is a sectional view taken on the line 10-10 in FIG. 4,

[0023]FIG. 11 is a perspective view of a center section of the presentinvention,

[0024]FIG. 12 is a partially sectional plan view of a second embodimentof the axle driving unit, from which an upper half housing is removed,

[0025]FIG. 13 is a sectional view taken on the line 13-13 in FIG. 12,

[0026]FIG. 14 is a sectional view taken on the line 14-14 in FIG. 12,

[0027]FIG. 15 is a sectional view taken on the line 15-15 in FIG. 12,

[0028]FIG. 16 is a perspective view of a center section of the secondembodiment,

[0029]FIG. 17 is a partially sectional plan view of a third embodimentof the axle driving unit, from which an upper half housing is removed,

[0030]FIG. 18 is a sectional view taken on the line 18-18 in FIG. 17,

[0031]FIG. 19 is a perspective view of a center section of the thirdembodiment,

[0032]FIG. 20 is a sectional side view of a fourth embodiment of theaxle driving unit,

[0033]FIG. 21 is a sectional plan view taken on the line 21-21 in FIG.20,

[0034]FIG. 22 is a sectional front view taken on the line 22-22 in FIG.21,

[0035]FIG. 23 is a sectional side view of a fifth embodiment of the axledriving unit,

[0036]FIG. 24 is a sectional plan view taken on the line 24-24 in FIG.23,

[0037]FIG. 25 is a sectional front view taken on the line 25-25 in FIG.23,

[0038]FIG. 26 is a sectional side view of a sixth embodiment of the axledriving unit,

[0039]FIG. 27 is a sectional plan view taken on the line 27-27 in FIG.26,

[0040]FIG. 28 is a sectional front view taken on the line 28-28 in FIG.26,

[0041]FIG. 29 is a sectional side view of a seventh embodiment of theaxle driving unit,

[0042]FIG. 30 is a sectional plan view taken on the line 30-30 in FIG.29, and

[0043]FIG. 31 is a sectional front view taken on the line 31-31 in FIG.29.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] In the following description of the various embodiments,description of parts designated with the same reference numerals willnot be repeated, unless specifically noted otherwise. In FIGS. 1 through3, a lawn tractor of the present invention is so constructed that anengine E is loaded on the front of a body frame 1, left and right driven(or front) wheels 2 freely steerable are suspended under the front ofthe body frame. An axle driving unit provided with left and rightdriving (or rear) wheels 3L and 3R is suspended at the rear of bodyframe 1. A grass catcher 4 is mounted to the rear end of body frame 1,and a mower 5 is attached beneath the body of the tractor between thefront and rear wheels through an elevation device (not shown). Mower 5is connected at a rear discharge port 5 a thereof with an inlet port ofcatcher 4 through a chute 6. Chute 6 extends slantwise upwardly from therear discharge port 5 a of the mower 5, passes laterally or to the sideof the axle driving unit and between the left and right rear drivingwheels 3L and 3R so as to be connected to the inlet of catcher 4.Accordingly, lawn grass cut by mower 5 is blown rearwardly to passbetween left and right rear driving wheels 3L and 3R through chute 6,and is then stored in catcher 4. The lawn tractor preferably includes aheight-adjustable seat that can be raised and lowered.

[0045] As shown in FIG. 1, two pulleys 8 and 9 are fixed onto an outputshaft 7 of engine E. Pulley 8 transmits a driving force through a belt10 to a third pulley 12 fixed onto an input shaft 11 of mower 5, therebyrotating cutter blades 5 b of mower 5 (see FIG. 2). The other pulley 9is adapted to transmit a driving force through a belt 13 to a fourthpulley 15 fixed onto a pump shaft or input shaft 29, projecting upwardlyfrom a housing for the axle driving unit. Reference numeral 16designates a cooling fan fixed to pulley 15 in order to cool the axledriving unit.

[0046] As shown in FIG. 3, the axle driving unit is suspended from afirst mounting member 1 a and a second mounting member 1 b, both partsof body frame 1. The axle driving unit is eccentrically disposed towardone of the two sides of body frame 1. FIG. 3 shows the axle driving unitdisposed in a position displaced toward driving wheel 3L relative to thecenter of the space between left and right driving wheels 3L and 3R. Theleft side of the housing of the axle driving unit is fixed to firstmounting member 1 a, and the right side to second mounting member 1 bthat downwardly extends from a laterally intermediate portion of firstmounting member 1 a. As shown in FIG. 3, body frame 1 of the tractorincludes first mounting member la provided longitudinally of body frame1 and at a portion adjacent to the inside of driving wheel 3L. Thesecond mounting member 1 b is suspended from about the center of thespace between driving wheels 3L and 3R. A bearing 20 is provided at aportion of body frame 1 adjacent to the inside of driving wheel 3R.

[0047] The housing for the axle driving unit comprises an upper halfhousing 21 and a lower half housing 22 joined to each other through aperipheral joint or junction surface. When the housing is mounted in anoperating position on body frame I of the tractor, the joint surface issubstantially horizontally disposed.

[0048] Shorter first axle 17 projects from the left side of the housingfor the axle driving unit, and longer second axle 18 projects from theright side of the housing. Driving wheel 3L mounts at one axial end offirst axle 17, and driving wheel 3R mounts at one axial end of secondaxle 18.

[0049] A first mounting boss 210 a is formed at a portion of the axledriving unit housing positioned near the distal portion (portion closestto the axle driving unit) of first axle 17, and a second mounting boss210 b is formed at the portion of the housing positioned near the distalportion of second axle 18.

[0050] First mounting member la is connected to first mounting boss 210a, and second mounting member 1 b is connected to second mounting boss210 b. Thus, the housing is eccentrically mounted in the working oroperating position, offset to one side toward driving wheel 3L. Such alayout ensures a sufficiently wide space between the axle driving unithousing and driving wheel 3R so that chute 6 can be offset from thecenter of the tractor body. As a result, the axle driving unit and chute6 can be arranged laterally, side by side each other within body frame1. This enables chute 6 to longitudinally extend within body frame 1.

[0051] Second axle 18 is supported at the distal portion thereof (18 a)by the housing, and at an intermediate portion of a longer portion (18b) projecting outwardly from the housing by a bearing 20. Hence, thedistance between the bearing for supporting the distal portion of firstaxle 17 and that for supporting the distal portion of second axle 18 canbe greatly reduced, thereby reducing the width W of the axle drivingunit housing. Consequently, chute 6 can be designed with a relativelyincreased cross-sectional area.

[0052] Alternatively, second axle 18 may be formed as one long axle.However, it is favorable for assembly of the axle driving unit andfacilitation of transportation to divide axle 18 into part 18 asupported at the housing, and part 18 b supported by bearing 20, asshown in FIG. 3. Parts 18 a and 18 b are connected by a coupling 19.

[0053] FIGS. 4-11 show the construction of an axle driving unit forspeed-change-driving rear driving wheels 3L and 3R. The housing of theaxle driving unit is formed by connecting upper half housing 21 andlower half housing 22 with each other. Lubricating oil is charged intothe housing, and is used as operating oil for a hydraulic stepless speedchange transmission T to be discussed below. First axle 17 and part 18 aof the second axle are rotatably supported in upper half housing 21positioned above the joint surface. As shown in FIG. 10, cylindricalbores 211 are formed at left and right side walls of upper half housing21 to form first bearing supports, respectively. Rolling bearings 100fitted into cylindrical bores 211 support the distal portion of firstaxle 17 and part 18 a of second axle 18, cylindrical bores 211 beingclosed at their outer ends with oil seals.

[0054] As best seen in FIG. 10, semicircular concave circular-arcsurfaces 212 are formed on the inner surface of an upper wall of upperhalf housing 21. On the inner surface of lower half housing 22 areintegrally formed projections 220 that project beyond the joint surface.Semicircular concave circular-arc surfaces 221 are formed at the endsurfaces of projections 220 that are positioned opposite to concavesurfaces 212, respectively, to form a pair of second bearing holders.Bushings 101 are inserted into the second bearing holders, so thatbushings 101 support the base ends of first axle 17 and part 18 a ofsecond axle 18, respectively.

[0055] As shown in FIG. 10, concave circular-arc surfaces 213 larger inradius than surfaces 212 are formed in concave circular-arc surfaces212, and concave circular-arc surfaces 222 larger in radius thansurfaces 221 are formed in concave circular-arc surfaces 221. Concavecircular-arc surfaces 213 and 222 are combined to form annular cavities.Rolling bearings (not shown) may be built-in to the cavities, instead ofthe aforesaid bushings 101, to support the base ends of first and secondaxles 17 and 18. The choice of bushings or bearings depends upon thesize of the load applied to axles 17 and 18. When the load is small,bushings 101, as shown in the embodiment of FIG. 10, are used to reducemanufacturing cost. When the load is large, the rolling bearings (notshown) are used to increase the support strength for the axles.

[0056] As shown in FIG. 10, first axle 17 and part 18 a of second axle18 abut concentrically against each other in the housing, differentiallyconnected to each other by a differential gear 23 contained in thehousing. Axle 17 and part 18 a of axle 18 project laterally outwardlyfrom the housing.

[0057] As best seen in FIGS. 8 and 10, an input gear 48 larger in widththan differential gear 23 has at the center a through-bore 480. The baseends of first axle 17 and part 18 a of second axle 18 are inserted intothrough-bore 480 to be supported by input gear 48. Bevel gears 49,spline-engaged with first axle 17 and part 18 a of second axle 18, andinput gear 48 prevent axial movement of the axles. Pinions 50 engageablewith bevel gears 49, and through-bores 481 for containing thereinpivotal pins 51 for pinions 50, are provided at both sides of input gear48. A flat portion formed at the circumferential surface of the end ofeach pivotal pin 51 abuts against a flat portion provided at eachthrough-bore 481, thereby restraining each pivotal pin 51 from rotating.Accordingly, differential gear 23 is formed from a smaller number ofparts.

[0058] The front portions (portions toward the front or forward end ofthe lawn tractor) of upper and lower half housings 21 and 22 areenlarged in a direction perpendicular to the longitudinal axes of theaxles. The housing of the axle driving unit is therefore longer (lengthL1) than it is wide (width W; see FIG. 4). A center section 25 for ahydraulic stepless speed change transmission T is mounted in theenlarged region. As shown in FIG. 11, center section 25 is a single andelongated piece having an upper surface 250 and a side surface 251 whichare adjacent and perpendicular to each other. A pump mounting surface 40is formed at the front portion (toward the front or forward end of thelawn tractor) of upper surface 250 for mounting thereon a hydraulicpump. At the rear portion of side surface 251 a motor mounting surface41 is formed for mounting a hydraulic motor. As shown in FIG. 8, pumpmounting surface 40 and motor mounting surface 41 are partiallyoverlapped with each other by a longitudinal length OL. The center ofmotor mounting surface 41 extends in parallel to pump mounting surface40 and is offset downwardly therefrom by a height H1.

[0059] As shown in FIG. 11, housing mounting faces 42 are formed onupper surface 250 of center section 25, approximately level withmounting surface 40. Therefore, housing mounting faces 42 can be groundwhen pump mounting surface 40 is ground, so that the processing time forthe pump mounting surface can be reduced. Bolt insertion bores areprovided at housing mounting faces 42 and center section 25 is fixed tothe inner wall of the enlarged region of upper half housing 21 throughconnecting bolts inserted into the bores. Pump mounting surface 40 ofcenter section 25 extends horizontally with respect to the axles, and isdisposed spaced apart from the axles. Motor mounting surface 41 extendsvertically with respect to the axles, and is disposed in proximity tothe axles.

[0060] Alternatively, pump mounting surface 40 and motor mountingsurface 41 may be provided integral to the inner wall by increasing thethickness of the inner wall in the enlarged region of lower half housing22. However, as shown in this embodiment, it is preferable to use centersection 25 separate from the housing to facilitate processing of thehousing, and to prevent oil from leaking out of the housing.

[0061] As shown in FIG. 5, a valve plate 102 is mounted onto pumpmounting surface 40. A cylinder block 36, constituting the hydraulicpump, is rotatably disposed on valve plate 102. Pistons 36 a are fittedinto a plurality of cylinder bores of cylinder block 36, forreciprocating movement through biasing springs. Pump shaft 29 engageswith a spline bore provided on the rotary axis of cylinder block 36.Pump shaft 29 is rotatably supported by upper half housing 21 and pumpmounting surface 40. Pulley 15 is fixed to a projection of pump shaft 29projecting outwardly from upper half housing 21. The heads of pistons 36a abut against a thrust bearing 28 a of a movable swash plate 28,thereby forming an axial piston type variable displacement hydraulicpump. Alternatively, the hydraulic pump may be of a radial piston typeor a gear type.

[0062] Pump shaft 29 is inserted into a longitudinally extendingthrough-bore formed at the axial center of movable swash plate 28. Aconvex circular-arc surface is formed at the rear of movable swash plate28, and slidably contacts with a concave circular-arc surface formed atthe inner surface of the upper wall of upper half housing 21. As aresult, movable swash plate 28 is movable in a longitudinal slantwisedirection along the concave circular-arc surface. As movable swash plate28 moves with respect to the rotary axis of cylinder block 36 along thecontact surface, the amount and flow direction of oil discharged fromthe hydraulic pump changes. As shown in FIG. 5, a control shaft 35 formovably operating movable swash plate 28 extends horizontally and isrotatably supported by a lid 38 that closes a side opening of upper halfhousing 21. At an outer end of control shaft 35 is fixed a control lever35 a that is connected in association with a speed change operating tool(not shown). At an inner end of control shaft 35 is fixed a base of aswinging arm 35 b. A ball 37, fixed to the utmost end of swinging arm 35b, engages through a joint block with an engaging groove 28 b of movableswash plate 28, control shaft 35 being rotated for movement of movableswash plate 28.

[0063] Movable swash plate 28 shown in this embodiment is of a cradletype that moves slantwise along the concave circular-arc surface of theinner surface of the upper wall of upper half housing 21. To enable atrunnion-type swash plate to be mounted instead of cradle-type swashplate 28, a bearing bore is positioned on the same axis as control shaft35 at a portion of the inner wall of upper half housing 21. Where thetrunnion-type movable swash plate is used, each trunnion shaft issupported by the bearing bore and lid 38. The cradle-type movable swashplate is advantageous in that it is inexpensive to produce, while thetrunnion-type is advantageous in that it requires a decreased operatingforce. Swash plates of both types are easily exchangeable.

[0064] Referring to FIG. 6, a valve plate 103 is mounted onto motormounting surface 41 formed on side surface 251 of center section 25. Acylinder block 44 of the hydraulic motor is rotatably disposed on plate103. A plurality of pistons 44 a are fitted for reciprocating movementinto a plurality of cylinder bores of cylinder block 44.

[0065] The heads of pistons 44 a abut against a thrust bearing 45 a at afixed swash plate 45, fixed between upper half housing 21 and lower halfhousing 22. A motor shaft 24 engages with a spline bore provided on therotary axis of cylinder block 44 to form an axial-piston type fixeddisplacement hydraulic motor. Alternatively, the hydraulic motor may beof a radial piston type or a gear type.

[0066] The rotation axis of cylinder block 44 is positioned in the sameplane as the joint surface of the upper and lower half housings. One endof motor shaft 24 is supported by motor mounting surface 41, the otherend being supported by a bearing sandwiched between upper half housing21 and lower half housing 22.

[0067] When the hydraulic pump and the hydraulic motor are disposed on acenter section having the configuration described above, pump shaft 29and motor shaft 24 are perpendicular to each other. Pump shaft 29 isoffset from motor shaft 24 by a length L2 in the direction apart fromthe axles (see FIG. 8).

[0068] As shown in FIGS. 4, 9, and 11, a pair of kidney-shaped ports 40a and 40 b is open on pump mounting surface 40 of center section 25 totake in or discharge oil in cylinder block 36. A pair of kidney-shapedports 41 a and 41 b is also open on motor mounting surface 41 to take inor discharge oil in cylinder block 44. Within center section 25 areprovided a straight oil passage 25 a and an L-like-shaped oil passage 25b for connecting kidney-shaped ports 40 a and 41 a, and 40 b and 41 bwith each other, respectively, to circulate the operating oil betweenthe hydraulic pump and hydraulic motor, thereby making a closed circuit.

[0069] The hydraulic pump and hydraulic motor are fluidly connected witheach other through the above-mentioned closed circuit, and thecombination of these members forms a hydraulic stepless speed changetransmission. Capacity of the hydraulic pump is changed by rotatablyoperating control lever 35 a, thereby enabling the hydraulic motor toobtain stepless output rotation.

[0070] Operating oil supply means is provided for replenishing oil thathas leaked out from center section 25. The supply means may be thehydraulic pump itself, or a charge pump 31.

[0071] Charge pump 31, as shown in FIGS. 5 and 7, is a trochoid pumpwhich is contained in a charge pump casing 30 attached to a charge pumpmounting surface 43 formed on the lower surface of center section 25. Awave washer 34 is interposed between a stepped portion at the outerperiphery of charge pump casing 30, and a bottom surface of a lid 33that closes an opening 223 in lower half housing 22. Wave washer 34biases charge pump 31 so that charge pump 31 is in contact with chargepump mounting surface 43. The lower end of pump shaft 29 passes throughcenter section 25 and projects from charge pump mounting surface 43, anda pin is mounted on shaft 29. An engaging bore is open at the center ofan internal gear of charge pump 31. The lower end of pump shaft 29 isinserted into the engaging bore, and pump shaft 29 engages with theinternal gear. Charge pump 31 is fixed to the lower end of pump shaft 29and is driven by pump shaft 29.

[0072] Charge pump casing 30 is disposed in an oil sump formed by thehousing. A suction port 30 a of charge pump 31 is open at the lowersurface of charge pump casing 30. Suction port 30 a connects with theoil sump in the housing through a groove 33 a formed by partiallycutting out a wave washer mounting portion at lid 33. An annular oilfilter 32 is fixed between charge pump mounting surface 43 and thebottom surface of lid 33. Since oil filter 32 surrounds charge pump 31and charge pump casing 30, existing oil is cleaned and then taken in bycharge pump 31 through groove 33 a and suction port 30 a. When oilfilter 32 is maintained and inspected, lid 33 is removed from lower halfhousing 22, and oil filter 32 is removed from the housing through anopening 223 of lower half housing 22, oil filter 32 being smaller inoutline than opening 223.

[0073] The pressure oil discharged from charge pump 31 is directlyguided into a supply oil passage 25 c open in charge pump mountingsurface 43. If the introduced pressure exceeds the pressurecorresponding to a biasing force of the wave washer biasing means, thepressure causes charge pump casing 30 to move away from or detach fromcharge pump mounting surface 43 against the biasing force of wave washer34. This creates a gap between charge pump 31 and charge pump mountingsurface 43. Pressure oil is then released in part from the gap into theoil sump to adjust its pressure below the biasing force of wave washer34. Charge pump 31 is detached from charge pump mounting surface 43 toadjust the discharge pressure below the biasing force while maintainingfluid communication between the discharge port and the oil supply port.

[0074] As shown in FIG. 8, due to the form of center section 25, pumpmounting surface 40 is positioned in the second plane P2 in upper halfhousing 21, in parallel to and spaced apart by a height H1 from thefirst plane P1 coincident with the joint surface of the housing. Hence,a wide space is formed between charge pump mounting surface 43positioned opposite to pump mounting surface 40, and the inner surfaceof the bottom of lower half housing 22. As a result, charge pump 31 andoil filter 32 can be contained in this space with ample room. Height H2from the axis of the axles to the bottom of lower half housing 22 isreduced to ensure sufficient ground clearance.

[0075] As shown in FIG. 9, check valves 50 are disposed at the open endsof oil passages 25 a and 25 b in the closed circuit of center section25. Check valves 50 mutually communicate at the inlet ports through onetransverse passage 25 d. Transverse oil passage 25 d communicates at theintermediate portion with a supply oil passage 25 c open at charge pumpmounting surface 43 of center section 25. Oil introduced from thedischarge port of charge pump 31 to supply oil passage 25 c reaches theinlet side of each check valve 50. The oil pressure pushes out checkvalves 50, positioned at the low pressure side of oil passages 25 a and25 b, so that oil is supplied from the outlet side into the closedcircuit.

[0076] Check valves 50 are slidably provided with push pins 51 thatproject outward from center section 25. An axial end of each push pin 51comes in contact with a single connecting plate 52 in the housing, and arelease rod 53 is fixed at the center of connecting plate 52. Releaserod 53 projects outwardly from upper half housing 21 at one end.Connecting plate 52 is outwardly biased by a spring 54 interposedbetween plate 52 and center section 25. Release rod 53 is manuallypushed in, so that push pins 51 simultaneously push out check valves 50so that the inlet port is in fluid communication with the outlet port.Hence, oil passages 25 a and 25 b communicate with each other throughtransverse oil passage 25 d, thereby enabling the hydraulic motor toidle.

[0077] As shown in FIGS. 4 and 8, motor shaft 24 is disposed in parallelto axles 17 and 18. A counter shaft 26 is provided between the axles andmotor shaft 24, and extends in parallel to the axles and motor shaft 24.A gear 240 is provided on motor shaft 24 and engages with a largerdiameter gear 46 fixed onto counter shaft 26. A smaller diameter gear 47on counter shaft 26 engages with a ring gear 48 of differential gear 23.Thus, a driving force output from motor shaft 24 is transmitted to axles17 and 18 through a gear system speed reduction transmission anddifferential gear 23.

[0078] As shown in FIG. 4, a braking friction plate 63 is fixed on motorshaft 24, an arm 64 is fixed to upper half housing 21, and a brakeactuator 65 is provided at one end of arm 64. An operating lever (notshown) is rotated to bring brake actuator 65 in press contact withbraking friction plate 63, thereby enabling motor shaft 24 to be braked.

[0079] The axis of counter shaft 26 is positioned in the first plane P1.It is supported at both axial ends by a pair of bearings interposedbetween upper half housing 21 and lower half housing 22.

[0080] As shown in FIG. 8, a pocket projects from the bottom of lowerhalf housing 22 to define height H2. The lower portion of largerdiameter gear 46 on counter shaft 26 is contained within this pocket.

[0081] The axes of axles 17 and 18 may be disposed in the first planeP1. However, it is preferable to dispose the axes above the first planeP1 as shown in this embodiment. This is because, even when a largediameter input gear 48 is used in order to enlarge the last gear ratio,the lower portion of input gear 48 will not extend lower than the lowerportion of larger diameter gear 46. Therefore, the pocket for gear 46need not be further enlarged, thereby enabling height H2 to be as smallas possible so that ground clearance is ensured.

[0082] As shown in FIG. 4, differential gear unit 23 is displaced in thehousing toward part 18 a of second axle 18. A space is thereby formed atone lateral side of a second axle holder. The larger diameter gear 46 ispartly disposed in this space so that the length of the housing does nothave to be increased.

[0083] As shown in FIG. 8, a partition 214 for covering an upper portionof input gear 48 is integrally formed in upper half housing 21 and anoil flow-through bore 215 is formed at partition 214. An opening 216 isformed at a portion of the upper wall of upper half housing 21positioned above partition 214, and covered with a cover member 55.Cover member 55 is provided with a breather 56 and an oil check rod 57that is also used as an oil charge plug. A predetermined amount of oilis charged into the housing through cover member 55 so that the boundaryof oil and air is formed in a space enclosed by partition 214 and covermember 55. Air mixed in the oil when charged into the housing iscollected in an air reservoir through oil flow-through bore 215.Partition 214 is filled at the lower portion with oil, so that, evenwhen the various gears rotate, the air in the air reservoir is scarcelymixed in the oil. When the axle driving unit is operated for a longtime, the oil volume expands. The volume of air in the air reservoirdecreases to accommodate the expanded volume of oil.

[0084] A second embodiment of the axle driving unit is shown in FIGS.12-16. The second embodiment is almost the same in construction as thefirst embodiment so that the same parts are designated with the samereference numerals and the description is omitted. As such, only threepoints of different construction will be described.

[0085] In the case where a lawn tractor includes a wide space underneaththe tractor where the mower is disposed, the enlarged region of thehousing is extended forwardly as much as possible. The width of thehousing is made as small as possible, thereby enabling the grass chuteto increase in volume.

[0086] Therefore, a first difference is to elongate the enlarged regionof the housing, and to suitably form center section 25 for such anenlarged region. Pump mounting surface 40 and motor mounting surface 41,formed on upper surface 250 and side surface 251 of center section 25,are formed so that motor mounting surface 41 laterally overlaps pumpmounting surface 40 by a length L2. As a result, center section 25 canbe contained in the enlarged region having width Wa (see FIG. 12).Cylinder block 36 of the hydraulic pump is disposed further away fromaxles 17 and 18 than in the first embodiment. Length L2 from pump shaft29 to motor shaft 24 is larger in this embodiment (see FIG. 13) than inthe first embodiment (see FIG. 8). There is no overlap OL in thisembodiment as there was in the first embodiment (see FIG. 8).

[0087] A third mount boss 210 c is provided at the utmost end of theenlarged region of the housing. Mount boss 210 c is connected to a thirdmounting member (not shown) hanging from body frame 1. Therefore, evenwhen the entire length L1 of the housing becomes larger, the axledriving unit remains in a proper operating position.

[0088] A second difference is with respect to motor shaft 24. As in thefirst embodiment, braking friction plate 63 is disposed on one end ofmotor shaft 24 that extends outwardly from the housing. The differencein this embodiment is that the other end of motor shaft 24 is providedwith a spline, and it extends into a through-open bore provided at thecenter of motor mounting surface 41. A bushing is interposed between thejoint surfaces of the housing to support a rotary shaft 59 (see FIG.12). The spline end of motor shaft 24 is spline-engaged with one end ofrotary shaft 59 so that the driving force of motor shaft 24 is taken outof the housing through rotary shaft 59.

[0089] The outer end of rotary shaft 59 is an indented spline. Brakingfriction plate 63 may be mounted on this end of rotary shaft 59, orrotary shaft 59 may be used as a power take-out shaft. If suchconstruction is not required, rotary shaft 59 can be removed and thebore formed at the joint surfaces of the housing can be closed by a sealcap.

[0090] A third difference is found in the movable swash plate of thehydraulic pump. Movable swash plate 60 of a trunnion-type is used inplace of that of a cradle-type. One trunnion shaft 60 a of movable swashplate 60 is supported by a lid 38 mounted to upper half housing 21, theother trunnion shaft 60 b being supported by a bearing bore provided atthe inner wall of upper half housing 21 (see FIG. 14). Trunnion shaft 60a projects outwardly from lid 38 and a control lever 35 a is mountedonto the projection.

[0091] A third embodiment of the axle driving is shown in FIGS. 17-19.The construction of the third embodiment compares to that of the secondembodiment as follows.

[0092] Center section 25 is not connected to upper half housing 21 bybolts, but inserted in part between upper half housing 21 and lower halfhousing 22. Therefore, center section 25 is positioned in the enlargedregion in a freestanding state. Housing mounting faces 42′ project fromthe left and right side surfaces 251. The upper surface of centersection 25 and the lower surface opposite thereto form housing mountingfaces. Since center section 25 is free-standing, bolts are not requiredso that assembly is simplified and manufacturing cost is lowered.

[0093] In order for center section 25 to be free-standing, pump shaft 29and motor shaft 24 are completely supported by the housing. Upper end ofpump shaft 29 is supported by a bearing 104 attached to upper halfhousing 21. Lower end of pump shaft 29 passes through mounting surface40 and charge pump mounting surface 43 and is supported by a bearing 105attached to lower half housing 22 (see FIG. 18). Motor shaft 24 passesthrough motor mounting surface 41 and the two ends are supported bybearings 106 and 107 inserted between both upper half and lower halfhousings 21 and 22 (see FIG. 17).

[0094] In the axle driving unit of an embodiment to be discussed below,as in the second and third embodiments, the enlarged region is made aselongated as possible in order to allow greater volume for the chute ofthe rear discharge lawn tractor.

[0095] A fourth embodiment of the axle driving unit will be described inaccordance with FIGS. 20, 21 and 22. A center section 25 ofsubstantially L-like shape in sectional side view is disposed in anelongated enlarged region extending across upper half housing 21 andlower half housing 22, and is fixed to upper half housing 21. A pumpmounting surface 40 is formed on a substantially horizontal uppersurface 250, and a motor mounting surface 41 on a substantially verticalside surface 251 of center section 25. Pump mounting surface 40 ispositioned apart from axles 17 and 18, and motor mounting surface 41 ispositioned near the axles. Pump shaft 29 extends substantiallyvertically with respect to axles 17 and 18, and motor shaft 24 extendssubstantially horizontally with and perpendicular to axles 17 and 18.

[0096] A movable swash plate 28 at the hydraulic pump is of acradle-type and uses the same operating mechanism as that in the firstembodiment so that it is manually controllable along a concavecircular-arc surface of an inner wall of upper half housing 21.

[0097] An oil filter 32 is interposed between the lower surface ofcenter section 25, opposite to pump mounting surface 40, and the innersurface of the bottom wall of lower half housing 22. Oil in the housingis filtered by oil filter 32 and guided to a supply port (not shown)open at the lower surface of center section 25.

[0098] A pair of kidney-shaped ports 40 a and 40 b open at pump mountingsurface 40, and a pair of kidney-shaped ports 41 a and 41 b open atmotor mounting surface 41 are connected with each other through a pairof substantially L-like-shaped oil passages 25 a and 25 b, respectively.As shown in FIG. 9, check valves are disposed at the open ends of oilpassages 25 a and 25 b. In this embodiment, operating oil is supplied byoperation of the hydraulic pump itself, but a charge pump as describedin the previous embodiments may alternatively be used.

[0099] The axis of motor shaft 24 is positioned in the same plane as thejoint surface of the housing. Motor shaft 24 is rotatably supported bybearings interposed between upper half housing 21 and lower half housing22.

[0100] First axle 17 and part 18 a of second axle 18 are rotatablysupported by lower half housing 22. Distal portions of first axle 17 andpart 18 a of second axle 18 are supported by bearings 100 held intocylindrical bores of lower half housing 22. The bases of axles 17 and 18are supported by bushings 101 disposed in lower half housing 22.Bushings 101 are fixedly interposed between legs 217, long enough toextend beyond the joint surface of the housing, and the concavecircular-arc surface of lower half housing 22 (see FIG. 22).

[0101] Differential gear 23 is displaced toward part 18 a of second axle18 in the housing. Motor shaft 24 is substantially perpendicular tofirst axle 17, and passes above axle 17 as it extends toward the rear ofthe housing. The utmost end of motor shaft 24 projects from the housing,and a braking friction plate 63 is attached to the utmost end of motorshaft 24.

[0102] A counter shaft 26, extending in parallel to axles 17 and 18, isdisposed at the rear of the housing. The axis of shaft 26 is positionedin the same plane as the joint surface of the housing. Shaft 26 isrotatably supported by bearings sandwiched between upper half housing 21and lower half housing 22.

[0103] Since motor shaft 24 and counter shaft 26 are substantiallyperpendicular to each other, a smaller diameter bevel gear 240 a onmotor shaft 24 and a larger diameter bevel gear 46 a, engageable withbevel gear 240 a, on counter shaft 26 are used to connect the shaftstogether in a driving manner. The driving force is transmitted from asmaller diameter gear 47 on counter shaft 26 to axles 17 and 18 througha ring gear 48 on differential gear 23.

[0104] A fifth embodiment of the axle driving unit will be described inaccordance with FIGS. 23, 24 and 25. Center section 25, disposed in anelongated enlarged region of the housing, has a substantially flat body.Center section 25 is attached to a side of upper half housing in asubstantially horizontal manner. Pump mounting surface 40 and motormounting surface 41 are formed on upper surface 250 of center section25; the former is positioned apart from axles 17 and 18 and the latteris positioned near the axles. Pump shaft 29 of the hydraulic pump andmotor shaft 24 of the hydraulic motor extend in parallel to each other,and are substantially vertical, being at a right angle to axles 17 and18.

[0105] A pair of kidney-shaped ports 40 a and 40 b open at pump mountingsurface 40, and a pair of kidney-shaped ports 41 a and 41 b open atmotor mounting surface 41 are connected to each other through a pair ofstraight oil passages 25 a and 25 b.

[0106] Movable swash plate 28 of the hydraulic pump is of a cradle-type,and is manually controllable along the concave circular-arc surface ofthe inner wall of upper half housing 21 by use of an operating mechanismas in the first embodiment. A fixed swash plate 45 of the hydraulicmotor is fixedly fitted into a concave formed at the inner wall of upperhalf housing 21.

[0107] Pump shaft 29 and motor shaft 24 are rotatably supported bybearings longitudinally juxtaposed at upper half housing 21, andbearings longitudinally juxtaposed at center section 25.

[0108] A counter shaft 26 is disposed in the same plane as the jointsurface of the housing. A pair of bearings for supporting counter shaft26 are sandwiched between a pair of legs 252 downwardly projecting fromthe lower surface opposite to motor mounting surface 41, and a pair oflegs 224 upwardly projecting from the inner surface of the bottom wallof lower half housing 22 (see FIG. 23). With this construction, there isno need for a bearing holding portion for counter shaft 26 to beprovided at the housing. Therefore, the width Wa of the enlarged regioncan be further restricted (see FIG. 24). One end of counter shaft 26projects outwardly from the housing for attachment of a braking frictionplate 63.

[0109] A substantially vertical motor shaft 24 passes downwardly throughcenter section 25. The lower end portion of motor shaft 24 is positionedjust above, and at about a right angle to, the axis of the axles (seeFIG. 25). A small diameter bevel gear 240 a is fixed on the lower end ofmotor shaft 24, and a larger diameter bevel gear 46, engageable withbevel gear 240 a, is fixed on counter shaft 26, thereby connectingshafts 24 and 26.

[0110] A driving force is transmitted from a smaller diameter gear 47 oncounter shaft 26 to a ring gear 48 of differential gear 23, differentialgear 23 being displaced toward part 18 a of axle 18 in the housing. Theaxes of axles 17 and 18 are positioned in the same plane as the jointsurface of the housing. The terminal and bore of first axle 17 aresupported only by bearing 100 and bushing 101 interposed between upperhalf housing 21 and lower half housing 22. Differential gear 23 iseccentrically disposed to further reduce the axial length of part 18 aof second axle 18 so that part 18 a of second axle 18 is supported byonly bushing 101 sandwiched between upper half housing 21 and lower halfhousing 22.

[0111] A sixth embodiment of the axle driving unit will be described inaccordance with FIGS. 26, 27 and 28. The construction is basically thesame as that of the fifth embodiment so that only the following fourpoints are described which are different from that of the fifthembodiment.

[0112] A first modified point is the position of braking friction plate63. The upper end of substantially vertical motor shaft 24 passesthrough the upper wall of upper half housing 21, and braking frictionplate 63 is mounted to this upper end. This allows the braking device tobe smaller and more compact because motor shaft 24 has a lowertransmitting torque than counter shaft 26. As a result, the axle drivingunit becomes smaller in width. Braking friction plate 63 is disposed onthe same side as pump shaft 29 that projects from the housing, and is inproximity to cooling fan 16. This enables friction plate 63 to beeffectively cooled by the ventilation from cooling fan 16. Theventilation from cooling fan 16 also blows away the dust collected onbraking friction plate 63.

[0113] A second modified point is with respect to center section 25. Oneleg 252 downwardly projects from the surface of center section 25opposite to motor mounting surface 41. Leg 252 and lower half housing 22support a bearing for the end of counter shaft 26, and a bearing at theother end of counter shaft 26 is sandwiched between upper half housing21 and lower half housing 22. Leg 252 may be formed separately fromcenter section 25 and fixed below its plane.

[0114] A third modified point is with respect to differential gear 23′.An input gear 48′ of differential gear 23′ is freely fitted on part 18 aof second axle 18, and is disposed in proximity to one side wall of thehousing, thereby considerably reducing the axial length of part 18 a ofsecond axle 18. A differential case 48 a is attached to the oppositeside wall of the housing. In differential case 48 a, the base ends offirst axle 17 and part 18 a of second axle 18 abut against each other.Side gears 49 engage with pinions 50 pivoted to the base sides of firstaxle 17 and part 18 a of second axle 18.

[0115] A fourth modified point is in the layout of first axle 17 andpart 18 a of second axle 18 and the construction of the housing supportwith respect to the joint surface of the housing. The axes of axles 17and 18 can be disposed in substantially the middle portion of the heightof the housing and still retain the balance of the axle driving unit.The protrusion formed in the bottom portion of lower half housing 22 forinput gear 48′ can thus be made smaller in volume to ensure sufficientheight from the ground.

[0116] A seventh embodiment of the axle driving unit will be describedin accordance with FIGS. 29, 30 and 31.

[0117] Center section 25, as in the fifth and sixth embodiments, issubstantially shaped like a flat plate, and mounted to upper halfhousing 21. The body of center section 25 is substantially horizontallydisposed in lower half housing 22. Pump mounting surface 40 is formed onthe substantially horizontal upper surface of center section 25 spacedapart from axles 17 and 18. Motor mounting surface 41 is formed on thesubstantially horizontal lower surface of center section 25 in proximityto axles 17 and 18.

[0118] Motor shaft 24 of the hydraulic motor is journalled at its upperend to center section 25, and at its lower end to lower half housing 22.If it is difficult to mount the hydraulic motor onto motor mountingsurface 41, the lower end of motor shaft 24 may be journalled to a fixedswash plate 45, and fixed swash plate 45 may be connected to the lowersurface of center section 25.

[0119] Motor shaft 24 extends in parallel to pump shaft 29, andsubstantially vertically passes through the upper wall of center section25. On the upper end of motor shaft 24 is fixed a smaller diameter bevelgear 240 a engageable with a larger diameter bevel gear 46 a on countershaft 26.

[0120] In order to support counter shaft 26 in the same plane as thejoint surface of the housing, a pair of bearings is provided between apair of legs 252′, upwardly projecting from the surface of the centersection opposite to motor mounting surface 41, and a pair of legs 218projecting from the inner wall of upper half housing 21.

[0121] Although several embodiments have been described, they are merelyexemplary of the invention and not to be construed as limiting, theinvention being defined solely by the appended claims and theirequivalents.

What is claimed is:
 1. An axle driving unit for use on a body framehaving first and second driving wheels, comprising: a housingeccentrically disposed on the body frame in proximity to the firstdriving wheel, said housing comprising an enlarged region; a first axlehaving a first longitudinal axis and supported by said housing formounting thereon the first driving wheel; a second axle having a secondlongitudinal axis and longer in length than said first axle for mountingthereon the second driving wheel, wherein said enlarged region extendssubstantially perpendicular to said first and said second axes of saidfirst and said second axles; and a speed change transmission disposedwithin said enlarged region, wherein said speed change transmissioncomprises a substantially vertical input shaft projecting outwardly fromsaid enlarged region, and an output shaft drivingly connected to saidfirst and said second axles.
 2. An axle driving unit according to claim1, wherein said speed change transmission further comprises: a hydraulicpump disposed in said enlarged region spaced apart from said first andsaid second axles; and a hydraulic motor disposed in said enlargedregion in proximity to said first and said second axles, wherein saidspeed change transmission is configured as a hydraulic stepless systemfor fluidly connecting said hydraulic pump and said hydraulic motor. 3.An axle driving unit according to claim 2, further comprising: a pumpmounting surface disposed in said enlarged region; a motor mountingsurface substantially perpendicular to said pump mounting surfacedisposed in said enlarged region; wherein said input shaft is connectedto said hydraulic pump and said hydraulic pump is mounted on said pumpmounting surface so that said input shaft is substantially vertical; andwherein said output shaft is connected to said hydraulic motor and saidhydraulic motor is mounted on said motor mounting surface so that saidoutput shaft is substantially horizontal.
 4. An axle driving unitaccording to claim 1, further comprising: bearing means disposed in saidhousing for supporting said first and said second axles, said bearingmeans comprising a pair of bearing holders, one of said pair supportingthe distal portion of said first axle and the other of said pairsupporting the distal portion of said second axle, wherein the distancebetween said pair of bearing holders defines the width of said housingto be less than the length of said housing including said enlargedregion.
 5. An axle driving unit according to claim 1, furthercomprising: a bearing device attached to the body frame for supportingan intermediate portion of said second axle.
 6. An axle driving unitaccording to claim 1, wherein said second axle comprises: a first axlepart; a second axle part for mounting thereon the second driving wheel;a coupling for connecting said first and said second axle parts; and abearing device attached to the body frame for supporting said secondaxle part.
 7. An axle driving unit for use on a body frame having firstand second driving wheels, comprising: a housing eccentrically disposedon the body frame in proximity to the first driving wheel, said housingcomprising an enlarged region; a first axle having a first longitudinalaxis and supported by said housing for mounting thereon the firstdriving wheel; a second axle having a second longitudinal axis andlonger in length than said first axle for mounting thereon the seconddriving wheel, wherein said enlarged region extends substantiallyperpendicular to said first and said second axes of said first and saidsecond axles; and a hydraulic stepless speed change transmissiondisposed in said enlarged region and drivingly connected to said firstand said second axles, wherein said hydraulic stepless speed changetransmission comprises, a hydraulic pump having a substantially verticalinput shaft, a hydraulic motor having an output shaft, and a centersection for fluidly connecting said hydraulic pump and said hydraulicmotor, said center section comprising a pump mounting surface spacedapart from said first and said second axles for mounting thereon saidhydraulic pump, and a motor mounting surface in proximity to said firstand said second axles for mounting thereon said hydraulic motor.
 8. Anaxle driving unit according to claim 7, wherein said center section isdisposed within said enlarged region so that said pump mounting surfaceis disposed within a substantially horizontal plane and said motormounting surface is disposed within a substantially vertical plane. 9.An axle driving unit according to claim 7, wherein said center sectionis disposed within said enlarged region so that said pump mountingsurface and said motor mounting surface are disposed within asubstantially horizontal plane.
 10. An axle driving unit according toclaim 8, wherein said pump mounting surface is formed to longitudinallyoverlap said motor mounting surface.
 11. An axle driving unit accordingto claim 7, further comprising: a housing mounting surface formed onsaid center section, wherein said housing comprises at least two housingparts joined along a junction surface parallel to said pump mountingsurface, said housing mounting surface sandwiched between said at leasttwo housing parts; a pair of input shaft bearings disposed in said atleast two housing parts, each of said pair supporting one end of saidinput shaft; a pair of output shaft bearings disposed in said at leasttwo housing parts, each of said pair supporting one end of said outputshaft; and wherein said center section defines an input shaft borethrough which said input shaft passes through said center section and anoutput shaft bore through which said output shaft passes through saidcenter section.
 12. An axle driving unit according to claim 7, furthercomprising: an oil sump formed within said housing, wherein the bottomwall of said housing defines an opening; a closed circuit disposed in adistal portion of said center section for circulating oil between saidhydraulic pump and said hydraulic motor, said closed circuit includingan oil supply port; an oil filter disposed within said oil sump forfiltering oil in said oil sump to be fed to said oil supply port,wherein said oil filter is smaller in outline than said opening; and alid detachably mounted to the outer bottom wall of said housing.
 13. Anaxle driving unit according to claim 7, further comprising: an oil sumpformed within said housing; an oil filter disposed within said oil sump;a closed circuit disposed in a distal portion of said center section forcirculating oil between said hydraulic pump and said hydraulic motor,said closed circuit including an oil supply port; a charge pump case; acharge pump driven by said input shaft for supplying oil in said oilsump to said oil supply port, said charge pump disposed within saidcharge pump case and including a suction port fluidly connected to saidoil filter, and a discharge port; a charge pump mounting surface formedon a surface of said center section opposite to said pump mountingsurface, wherein said oil supply port is open at said charge pumpmounting surface and said charge pump is mounted on said charge pumpmounting surface so that said discharge port is connected to said oilsupply port.
 14. An axle driving unit according to claim 13, furthercomprising: biasing means disposed between said charge pump case andsaid housing for biasing said charge pump to contact said charge pumpmounting surface in a detachable manner, wherein a discharge pressure ofsaid charge pump greater than the biasing force of said biasing meansdetaches said charge pump from contact with said charge pump mountingsurface to adjust said discharge pressure below the biasing force whilemaintaining fluid communication between said discharge port and said oilsupply port.
 15. An axle driving unit according to claim 7, furthercomprising: an oil sump formed within said housing, wherein said housingcomprises an upper half housing rotatably supporting said first and saidsecond axles, and a lower half housing; an oil filter disposed withinsaid oil sump; a charge pump mounting surface disposed on a surface ofsaid center section opposite to said pump mounting surface, wherein saidpump mounting surface is disposed within said upper half housing; aclosed circuit disposed within a distal portion of said center sectionfor circulating oil between said hydraulic pump and said hydraulicmotor, said closed circuit including a supply port; and a charge pumpdriven by said input shaft and disposed on said charge pump mountingsurface, said charge pump including a suction port for fluidlyconnecting said charge pump and said oil filter, and a discharge portfor fluidly connecting said charge pump and said supply port.
 16. Anaxle driving unit according to claim 15, wherein said oil filter isannular and surrounds said charge pump.
 17. A lawn tractor comprising: abody frame having two sides, a forward portion and a rear portion; aprime mover disposed on said body frame; a first driving wheel disposedon one of the two sides of said body frame; a second driving wheeldisposed on the other of the two sides of said body frame; a housingincluding an enlarged region, said housing eccentrically disposed towardone of the two sides of said body frame; a first axle projecting fromsaid housing for mounting thereon said first driving wheel; a secondaxle projecting from said housing for mounting thereon said seconddriving wheel, said second axle longer in length than said first axle; aspeed change transmission disposed within said enlarged region forinputting a driving force and changing the speed of the driving forcefor outputting to said first and said second axles; a mower disposedbeneath said body frame and driven by said prime mover; a catcherattached to the rear portion of said body frame; and a longitudinallyextending chute attached to said body frame, said chute guiding lawngrass cut by said mower into said catcher, wherein said enlarged regionextends toward the forward portion of said body frame in parallel tosaid chute.
 18. A lawn tractor according to claim 17, furthercomprising: a first mount boss disposed on a first side of said housingfrom which said first axle projects; a second mount boss disposed on asecond side of said housing from which said second axle projects; afirst mounting member attached to said body frame adjacent to said firstdriving wheel; a second mounting member attached to said body framebetween said first and said second driving wheels; and wherein saidfirst mount boss is coupled to said first mounting member and saidsecond mount boss is coupled to said second mounting member to therebymount said housing to said body frame in an operating position.
 19. Alawn tractor according to claim 18, wherein said body frame defines aspace for disposing therein said chute so that said chute extends abovesaid second axle.
 20. A lawn tractor according to claim 17, furthercomprising: a bearing device attached to said body frame adjacent tosaid second driving wheel for rotatably supporting an intermediateportion of said second axle.
 21. A lawn tractor according to claim 20,wherein said second axle comprises: a first axle part; a second axlepart for mounting thereon the second driving wheel, said second axlepart rotatably supported by said bearing device; and a coupling forconnecting said first and said second axle parts.
 22. A lawn tractoraccording to claim 17, further comprising: a pair of bearing holdersdisposed in said housing, one of said pair supporting the distal portionof said first axle and the other of said pair supporting the distalportion of said second axle, wherein the distance between said pair ofbearing holders defines the width of said housing to be less than thelength of said housing including said enlarged region.
 23. A lawntractor comprising: a body frame having two sides, a forward portion anda rear portion; an engine having a vertical crank shaft disposed on saidbody frame; a first driving wheel disposed on one of the two sides ofsaid body frame; a second driving wheel disposed on the other of the twosides of said body frame; a housing including an enlarged region, saidhousing eccentrically mounted to said body frame in proximity to saidfirst driving wheel; a first axle projecting from said housing formounting thereon said first driving wheel; a second axle projecting fromsaid housing for mounting thereon said second driving wheel, said secondaxle longer in length than said first axle; a speed change transmissiondisposed within said enlarged region and drivingly connected to saidfirst and said second axles, said speed change transmission including asubstantially vertical input shaft projecting from an upper surface ofsaid enlarged region for inputting a driving force into said speedchange transmission from said engine, wherein said input shaft isdisposed at the front of said enlarged region, eccentrically disposedtoward said first axle; a mower disposed beneath said body frame anddriven by said engine; a catcher attached to the rear portion of saidbody frame; and a longitudinally extending chute attached to said bodyframe for guiding lawn grass cut by said mower, wherein said enlargedregion extends toward the forward portion of said body frame in parallelto said chute.
 24. A lawn tractor according to claim 23, wherein saidspeed change transmission further comprises: a hydraulic pump disposedin said enlarged region spaced apart from said first and said secondaxles, wherein the rotary axis of said hydraulic pump is positioned onthe rotary axis of said input shaft; and a hydraulic motor disposed insaid enlarged region in proximity to said first and said second axles,wherein said speed change transmission is configured as a hydraulicstepless system for fluidly connecting said hydraulic pump and saidhydraulic motor.
 25. A lawn tractor according to claim 23, furthercomprising: bearing means disposed in said housing for supporting saidfirst and said second axles, said bearing means comprising a pair ofbearing holding members, one of said pair supporting the distal portionof said first axle and the other of said pair supporting the distalportion of said second axle, wherein the distance between said pair ofbearing holding members defines the width of said housing to be lessthan the length of said housing including said enlarged region.
 26. Alawn tractor according to claim 23, further comprising: a bearing deviceattached to said body frame adjacent to said second driving wheel forrotatably supporting an intermediate portion of said second axle.
 27. Alawn tractor according to claim 23, wherein said second axle comprises:a first axle part; a second axle part for mounting thereon the seconddriving wheel; a coupling for connecting said first and said second axleparts; and a bearing device attached to said body frame for supportingsaid second axle part.
 28. A lawn tractor according to claim 17, furthercomprising: a mower discharge port formed in said mower, wherein saidmower discharge port is eccentrically disposed toward the other of thetwo sides of said body frame away from said housing.